Composite autologous-allogeneic skin replacement: development and clinical application

Cultured skin substitutes reduce donor skin harvesting for closure of excised, full-thickness burns

OBJECTIVE

Comparison of cultured skin substitutes (CSS) and split-thickness skin autograft (AG) was performed to assess whether donor-site harvesting can be reduced quantitatively and whether functional and cosmetic outcome is similar qualitatively in the treatment of patients with massive cutaneous burns.

SUMMARY BACKGROUND DATA

Cultured skin substitutes consisting of collagen-glycosaminoglycan substrates populated with autologous fibroblasts and keratinocytes have been shown to close full-thickness skin wounds in preclinical and clinical studies with acceptable functional and cosmetic results.

METHODS

Qualitative outcome was compared between CSS and AG in 45 patients on an ordinal scale (0, worst; 10, best) with primary analyses at postoperative day 28 and after about 1 year for erythema, pigmentation, pliability, raised scar, epithelial blistering, and surface texture. In the latest 12 of the 45 patients, tracings were performed of donor skin biopsies and wounds treated with CSS at postoperative days 14 and 28 to calculate percentage engraftment, the ratio of closed wound:donor skin areas, and the percentage of total body surface area closed with CSS.

RESULTS

Measures of qualitative outcome of CSS or AG were not different statistically at 1 year after grafting. Engraftment at postoperative day 14 exceeded 75% in the 12 patients evaluated. The ratio of closed wound:donor skin areas for CSS at postoperative day 28 was significantly greater than for conventional 4:1 meshed autografts. The percentage of total body surface area closed with CSS at postoperative day 28 was significantly less than with AG.

CONCLUSIONS

The requirement for harvesting of donor skin for CSS was less than for conventional skin autografts. These results suggest that acute-phase recovery of patients with extensive burns is facilitated and that complications are reduced by the use of CSS together with conventional skin grafting.

Integra as a dermal replacement in a meshed composite skin graft in a rat model: a one-step operative procedure

BACKGROUND

Current use of Integra, the collagen-based dermal analogue, requires a two-step grafting procedure to achieve wound closure with an "ultrathin" autograft.

METHODS

A one-step operative procedure of meshed composite skin graft (MCSG) using Integra as a dermal template for a meshed split thickness autograft was developed in rats. The silicon layer of Integra was removed, the resulting dermal analogue was meshed (1:1.5), expanded, and placed on excised full thickness wound and covered with a meshed (1:1.5 or 1:6) split thickness autograft. Grafted wounds were dressed with BioBrane, Vaseline gauze, silver-impregnated nylon, or silver-nylon and direct current (SNDC). At scheduled intervals up to 3 months postgrafting, wounds were examined for epithelialization, collagen deposition and fibrosis, hair growth, and contraction. The results of wound closure and healing following the one-step procedure were compared with the outcome of the two-step grafting procedure where application of meshed Integra (step one) was followed in 14 days by removal of the silicon layer and application of the meshed autograft (step two).

RESULTS

The one-step procedure applied to meshed autograft/Integra (1:1.5/1:1.5) composite graft accelerated wound closure by 6-19 days when compared with the two-step procedure. At 3 months postgrafting, the contraction of the healed wound dressed with SNDC, BioBrane, or Vaseline gauze was reduced by 13-16% following the one-step procedure compared with the two-step procedure (p < 0.05). The one-step procedure allowed the expansion of the autograft layer to 1:6 while achieving wound healing results similar to grafting with 1:1.5 meshed autograft layer using the two-step grafting procedure.

CONCLUSION

Single-step application of meshed, thin, split thickness autograft over meshed Integra-derived dermal substitute allows more rapid wound closure with less contraction and more efficient use of graft donor skin than can be obtained with the commonly used two-step grafting procedure.

[Cultured epidermis for the treatment of severe burns. A 2-year study (18 patients)]

AIM OF THE STUDY

For fifteen years, Edouard Herriot Burn Center has been using cultured epidermis provided by an hospital Laboratory. This means of production results in great freedom for their application compared with the centers who have to buy the cultured epidermis. In order to evaluate our clinical results, a two-year study has been performed.

MATERIAL AND METHODS

Eighteen patients suffering acute burns were concerned. The average burned area was 68% of the total body surface (range 49 to 88). The average age was 31.6 years, ranging from 1 to 58, including two children. Even autologous or allogenic epidermis was used. In our series cultured epidermis was grafted according four different strategies. It was the preparation of the wound bed by skin allografts, the association of widely meshed auto-graft with cultured epidermis, the stimulation of the healing of extensive deep second degree burns with allogenic epidermis, and the coverage of skin auto-graft donor sites.

RESULTS

Two patients died. For the survivors, the average hospital stay was 60 days (range 22 to 90), and on average 70 days over 70% TBSA burns. Cultured epidermis allowed the definitive coverage of 17% of the total body surface of the patients. This study supports the importance of a careful preparation of the patient for the engraftment of cultured epidermis.

CONCLUSION

In our opinion, in spite of the difficulties of handling of cultured epidermis, they represent a precious means of coverage for the rapid and definitive healing of extensive burns over 70% TBSA.

Cryopreserved cultured epidermal allografts achieved early closure of wounds and reduced scar formation in deep partial-thickness burn wounds (DDB) and split-thickness skin donor sites of pediatric patients

Burn treatment in children is associated with several difficulties, e.g. available skin replacement is small, donor area could expand, and subsequent hypertrophic scar and contracture could become larger along with their physical growth. In order to have better clinical results, the authors prepared cryopreserved cultured epidermal allografts from excess epidermal cells of other patients, and applied the epidermal allografts to 55 children, i.e. 43 cases of deep partial-thickness burn wounds (DDB) due to scald burn and 12 cases with split-thickness skin donor sites. In the 43 DDB patients, epithelialization was confirmed 9.1+/-3.6 days (mean+/-S.D.) after treatment. In 10 of the 43 patients, epithelialization was comparable between the area which received the epidermal allografts (grafted area) and the area which did not receive the epidermal allografts but was covered with usual wound dressing (non-grafted area). As a result, epithelialization day was 7.9+/-1.7 in grafted areas and 20.5+/-2.3 in non-grafted areas. In the 12 patients with split-thickness skin donor sites, epithelialization was confirmed 6.3+/-0.9 days after treatment. Epithelialization of the grafted and non-grafted areas was comparable in 8 of the 12 patients, and it was 6.5+/-1.1 days and 14.1+/-1.6 days, respectively. In these 10 DDB patients and 8 split-thickness skin donor site patients, redness and scar formation were also milder in the grafted area. The 55 patients have been followed up for 1-8 years (mean, 4.75 years), and scar formation was suppressed in both DDB and split-thickness skin donor sites. These findings showed that cryopreserved cultured epidermal allografts achieve early closure of the wounds and good functional outcomes.

Initial experience with a composite autologous skin substitute

Patients with large burns are surviving in increasing numbers, but there remains no durable and reliable permanent skin replacement. After initial favorable small animal experiments, a pilot trial of a composite skin replacement was performed in patients with massive burns. A composite skin replacement (CSR) was developed by culturing autologous keratinocytes on acellular allogenic dermis. This material was engrafted in patients with massive burns and compared to a matched wound covered with split thickness autograft. With human studies committee approval, 12 wounds in 7 patients were grafted with CSR while a matched control wound was covered with split thickness autograft. These 7 children had an average age of 6.4+/-1.4 yr and burn size of 75.9+/-5.0% of the body surface. Nine wounds were acute burns and three were reconstructive releases. Successful vascularization at 14 days averaged 45.7+/-14.2% (range 0-100%) in the study wounds and 98+/-1% (range 90-100%) in the control sites (P<0.05). Reduced CSR take seemed to correlate with wound colonization. All children survived. While CSR did not engraft with the reliability of standard autograft, this pilot experience is encouraging in that successful wound closure with this material is possible, if not yet dependable. It is hoped that a more mature epidermal layer may facilitate engraftment, and trials to explore this possibility are in progress.

In vivo cultured skin composed of two-layer collagen sponges with preconfluent cells

Although various kinds of cultured skin substitutes have been developed, it takes several weeks to produce them before grafting. In their previous study, the authors succeeded in producing cultured skin easily in a short period of time by layering two collagen sponges. In the current study, to shorten this period even further, they grafted the cell-preconfluent artificial skin immediately after seeding the cells. They used two collagen sponges with different pore sizes and crosslink densities. They seeded 1,000,000 cells per square centimeter of fibroblasts and 1,000,000 cells per square centimeter of keratinocytes on the respective collagen sponges and grafted them on a full-thickness, excised wound on the back of severe combined immunodeficient mice. Two weeks after grafting, epithelium and dermislike tissue were formed. They then decreased the number of keratinocytes and grafted them. Four weeks after grafting, at seeding densities of 50,000 to 1,000,000 cells per square centimeter of keratinocytes, the preconfluent artificial skin took histologically, and human type IV and type VII collagen were stained immunohistochemically. This cell-preconfluent artificial skin composed of two-layer collagen sponges seems promising for widespread clinical use.

Extensive traumatic soft tissue loss: reconstruction in severely injured patients using cultured hyaluronan-based three-dimensional dermal and epidermal autografts

BACKGROUND

This report demonstrates the potential of two-stage autologous keratodermal grafting as a starting point for noninvasive reconstruction of extensive traumatic soft tissue defects.

METHODS

In three severely injured patients, skin biopsies for cell cultivation were taken. Cultured "neodermis" consisting of cultured autologous fibroblasts grown on biocompatible three-dimensional scaffolds made up of benzyl ester of hyaluronan was grafted on conditioned defect areas. After ingrowth of dermal substitutes, transplantation of cultured autologous keratinocytes on hyaluronan-based laser-perforated membranes was performed. Ten days later, a 0.2-mm thin, 1:6 meshed autograft was overlaid. Clinical follow-up, histologic, and immunohistochemical findings were documented.

RESULTS

Grafting with cultured autologous fibroblasts revealed a suitable dermal tissue replacement. Epithelialization was evident after transplantation of keratinocytes. Final closure of the defects with "normoelastic" tissue properties was achieved after thin mesh-grafting.

CONCLUSION

Preliminary findings with the described method seem to be very promising. As in all fields of tissue engineering, long-term studies and further follow-up are required.

Tissue-engineered product: allogeneic cultured dermal substitute composed of spongy collagen with fibroblasts

Recently, various types of allogeneic skin substitutes including cultured epidermal substitute (CES), cultured dermal substitute (CDS), and cultured skin substitute (CSS), which are composed of keratinocytes and/or fibroblasts as the cellular component(s), have been used as biological wound dressings. In our study, the allogeneic CDS was prepared by plating fibroblasts on a spongy collagen. The clinical evaluation was conducted using fresh or cryopreserved allogeneic CDS. In 145 of our clinical cases, 95% (138/145) of various wounds were evaluated as achieving good or excellent results, including 96% (22/23) of deep dermal burns (DDB) and dermal burns (DB), 100% (53/53) of partial-thickness donor wounds, 91% (21/23) of traumatic skin defects, 100% (5/5) of pressure ulcers, 82% (9/11) of chronic skin ulcers, 100% (6/6) of coverage for debrided DB, and 92% (22/24) of coverage for autologous meshed graft. The results obtained in our study suggest that the allogeneic CDS is able to provide an effective therapy for patients with partial and/or full-thickness skin defects.

Demonstration of epidermal transfer from a polymer membrane using genetically marked porcine keratinocytes

The culture of keratinocytes on flexible membranes has been proposed as a means to simplify, accelerate and improve the efficiency with which proliferating cells are delivered to full thickness or non-healing skin defects. However, there have been no studies that monitor the transfer of cells from such membranes to the wound bed. We have used a porcine model of lacZ gene marked cultured autologous keratinocyte grafting to demonstrate unambiguously the transfer of cultured cells to cutaneous wounds from the EpiGen polymer membrane developed by Smith & Nephew Group plc. Full thickness wounds enclosed within rigid chambers were first grafted with autologous de-epidermalised dermis (DED). Keratinocytes were cultured on EpiGen membranes and applied to the wound beds 7 days after the DED grafts. Epidermal remnants persist within the DED and the resultant epidermis is therefore, a mixture of wound regeneration and delivered cultured cells. Unequivocal evidence for keratinocyte transfer from the membrane was obtained through the observed macroscopic surface staining for lacZ transduced cells and lacZ positive cells detected in sections through deeper layers of epidermal tissue. This method offers a general approach for evaluating the efficiency of keratinocyte delivery using upside-down flexible membrane transfer.

Take percentage and conditions of cultured epithelium were improved when basement membrane of the graft was maintained and anchoring mesh was added

To achieve a higher take rate for epithelial grafts, this study investigated grafting techniques. Seventy-seven nude mice received flap grafting in which cultured human epithelium was grafted inside the flap, and 55 nude rats received transplantation of epithelium to a full-thickness skin defect. In each group, four models were studied, including model 1, in which epithelium was cultured with the conventional method; model 2, in which epithelium was cultured with fibrin gel to avoid sheet damage, then absorptive mesh was incorporated into the epithelium for anchoring to the graft bed; model 3, in which epithelium was cultured with fibrin gel and combined with absorptive mesh and artificial dermis containing fibroblasts; and model 4, in which the model 2 epithelium was grafted after artificial dermis was transplanted. The take for these models was evaluated grossly and histologically. The results show that the take percentage of models 2 and 3 was significantly higher than that of model 1 (conventional epithelium) and that there was no significant difference between model 3 (simultaneous grafting) and model 4 (two-step grafting). The difference in the take percentages of the grafts to the flap and to the full-thickness skin defect was also insignificant. In immunohistochemistry, human keratin appeared in all epidermis layers and diversification of the layer was observed in models 2, 3, and 4. In these three models, type IV collagen appeared in the basal layer and the formation of basal membrane was confirmed. These findings suggest that epithelia cultured on fibrin gel and combined with absorptive mesh could be used in a new technique for better, more stable take.

Long-term regeneration of human epidermis on third degree burns transplanted with autologous cultured epithelium grown on a fibrin matrix

BACKGROUND

Extensive third degree burn wounds can be permanently covered by the transplantation of autologous cultured keratinocytes. Many modifications to Green and colleagues' original technique have been suggested, including the use of a fibrin matrix. However, the properties of the cultured cells must be assessed using suitable criteria before a modified method of culture for therapeutic purposes is transferred to clinical use, because changes in culture conditions may reduce keratinocyte lifespan and result in the loss of the transplanted epithelium.

METHODS

To evaluate the performances of human keratinocytes grown on a fibrin matrix, we assay for their colony-forming ability, their growth potential and their ability to generate an epidermis when grafted onto athymic mice. The results of these experiments allowed us to compare side by side the performance for third degree burn treatment of autologous cultured epithelium grafts grown according to Rheinwald and Green on fibrin matrices with that of grafts grown directly on plastic surfaces.

RESULTS

We found that human keratinocytes cultured on a fibrin matrix had the same growth capacity and transplantability as those cultured on plastic surfaces and that the presence of a fibrin matrix greatly facilitated the preparation, handling, and surgical transplantation of the grafts, which did not need to be detached enzymatically. The rate of take of grafts grown on fibrin matrices was high, and was similar to that of conventionally cultured grafts. The grafted autologous cells are capable of generating a normal epidermis for many years and favor the regeneration of a superficial dermis.

CONCLUSION

We have demonstrated that: 1) fibrin matrices have considerable advantages over plastic for the culture of skin cells for grafting and that it is now possible to generate and transplant enough cultured epithelium from a small skin biopsy to restore completely the epidermis of an adult human in 16 days; and 2) the generated epidermis self-renews itself for years. The use of fibrin matrices thus significantly improves the transplantation of cultured epithelium grafts for extensive burns as recently demonstrated in a follow-up work.

The effect of a tissue engineered bilayered living skin analog, over meshed split-thickness autografts on the healing of excised burn wounds. The Apligraf Burn Study Group

The potential of Apligraf(R) (Graftskin) (Organogenesis Inc., Canton, MA), to improve cosmetic and functional outcomes when applied over meshed split thickness autografts was evaluated in a multicenter, randomized within patient controlled clinical trial. Experimental treatment sites had Apligraf(R) placed over meshed autograft while control sites were treated with meshed autograft covered with meshed allograft, or meshed autograft not covered by a biologic dressing. Forty patients were entered into this study of which 38 were evaluable. There was no difference in the percent take of autograft in the presence or absence of Apligraf(R) or in the median number of days to greater than 75% take of autograft. At the completion of the study 22 (58%) of the Apligraf(R) sites were rated superior to the control sites by the investigators, 10 (26%) were rated equivalent to the control and six (16%) were rated worse than control (p=0. 0037). Pigmentation, in the Apligraf(R) group was significantly better than control and by month 24, 17 (45%) Apligraf(R) sites had normal pigmentation compared with five (13%) control sites (p=0. 0005). Similarly by month 24, 18 (47%) patients had normal vascularity at the Apligraf(R) site compared with six (16%) patients at the control site. Improvements in pliability were observed with Apligraf(R) over control treatment within the first week of treatment. At month 24, 23 (61%) patients had normal height at the Apligraf(R) site compared to 14 (37%) with normal height at the control site (p=0.0117). Vancouver burn scar scores were shown to be statistically better at Apligraf(R) sites compared to control at all time points from week 1 to month 24. These results indicate that Apligraf(R) is a suitable and clinically effective treatment for burn wounds when applied over meshed autografts. Furthermore, cosmetic and functional advantages with Apligraf(R) were demonstrated when applied over meshed autograft compared to the current standard treatments of meshed autografts.

Biomaterial-microvasculature interactions

The utility of implanted sensors, drug-delivery systems, immunoisolation devices, engineered cells, and engineered tissues can be limited by inadequate transport to and from the circulation. As the primary function of the microvasculature is to facilitate transport between the circulation and the surrounding tissue, interactions between biomaterials and the microvasculature have been explored to understand the mechanisms controlling transport to implanted objects and ultimately improve it. This review surveys work on biomaterial-microvasculature interactions with a focus on the use of biomaterials to regulate the structure and function of the microvasculature. Several applications in which biomaterial-microvasculature interactions play a crucial role are briefly presented. These applications provide motivation and framework for a more in-depth discussion of general principles that appear to govern biomaterial-microvasculature interactions (i.e., the microarchitecture and physio-chemical properties of a biomaterial as well as the local biochemical environment).

Skin grafting

No longer an option of last resort, skin grafting has become a technique that is routinely and sometimes preferentially considered as skin replacement for burns, chronic ulcers, and skin defects after cutaneous surgical procedures. When selected as the best alternative for wound closure, autologous skin grafts are commonly considered the gold standard. Availability of autologous grafts is a major obstacle, however, and the search for a manufactured skin replacement has continued. In cases in which autologous grafts cannot be performed, skin substitutes have become an attractive alternative.

Accelerated healing with a mesh autograft/allodermal composite skin graft treated with silver nylon dressings with and without direct current in rats

PURPOSE

Evaluation of the healing and persistence of a meshed composite skin graft applied without immunosuppression.

METHODS

The contraction of wounds grafted with 9:1 split-thickness autograft/1.5:1 allodermal mesh composite skin grafts (auto/allo MCSGs) was investigated. No immunosuppressive agent was applied. Male ACI rats and female Lewis rats reciprocally served as allodermis graft donors and recipients. Autograft/dermal autograft and allograft/dermal allograft MCSGs were the controls.

RESULTS

AT 3 months after grafting, when epithelized auto/allo MCSG wounds were measured by computerized morphometric analysis, the silver nylon (SN) dressing group displayed less contraction than the Vaseline (petroleum jelly) dressing group (p < 0.003), and direct current treatment (SNDC) was more effective than SN (p < 0.005). The histologic structures of the hair follicles appear to confine the rejection process to the allogeneic follicles of the graft. The focal nature of the rejection process and the relatively low antigenicity of the dermal matrix allowed the survival of the allodermis layer. Although direct current significantly enhanced MCSG healing, SN and SNDC were not the immunosuppressive agents that were confirmed.

CONCLUSION

This type of MCSG can heal without immunosuppressive treatment.

Cost-efficacy of cultured epidermal autografts in massive pediatric burns

OBJECTIVE

To assess the efficacy of cultured epidermal autografts (CEA) for closure of burn wounds in pediatric burn patients with full-thickness burns of more than 90% total body surface area.

SUMMARY BACKGROUND DATA

Paucity of donor sites in massive burns makes the use of expanded skin of paramount importance. CEA techniques have been used in burned patients with differing and controversial results. The true impact and the efficacy of such techniques in massive burns remain uncertain.

METHODS

Patients with full-thickness burns of more than 90% body surface area treated between May 1988 and May 1998 were studied. Patients grafted with CEA were compared with patients grafted with conventional meshed autografts. Rates of death and complications, length of hospital stay (LOS), hospital cost, acute readmissions for reconstruction, and quality of scars were studied as outcome measures.

RESULTS

Patients treated with CEA had a better quality of burn scars but incurred a longer LOS and higher hospital costs. Both groups had comparable readmissions for open wounds, but patients treated with CEA required more reconstructive procedures during the first 2 years after the injury. The incidence of sepsis and pneumonia in both groups was comparable.

CONCLUSIONS

Conventional meshed autografts are superior to CEA for containing hospital cost, diminishing LOS, and decreasing the number of readmissions for reconstruction of contractures. However, the use of CEA provides better scar quality such that perhaps future research should focus on bioengineered dermal templates to promote take and diminish long-term fragility.

Cultured epithelial autografts in extensive burn coverage of severely traumatized patients: a five year single-center experience with 30 patients

OBJECTIVE

We report recent five-year experience in a large, single center series of severely burned and otherwise traumatized patients given cultured epithelial autografts (CEA) from a single commercial laboratory.

SUMMARY BACKGROUND DATA

Initial optimism over CEA application has been tempered by subsequent reports asserting that this modality is unreliable and expensive. Discussion continues over its clinical role.

METHODS

From 1991 to 1996, CEA were applied to a mean 37+/-17% of total body surface area (TBSA) of 30 patients. These patients had 78+/-10% average burn size, 65+/-16% average third-degree burn size, 90% prevalence of endoscopically confirmed inhalation injury and 37% prevalence of other serious conditions.

RESULTS

CEA achieved permanent coverage of a mean 26+/-15% of TBSA, an area greater than that covered by conventional autografts (a mean 25+/-10% of TBSA). Survival was 90% in these severely burned and otherwise traumatized patients. Final CEA take was a mean 69+/-23%. In subset analyses, only younger age was significantly associated with better CEA take (p = 0.0001 in univariate analysis, p<0.04 in multivariate analysis, Student's t-test).

CONCLUSIONS

Epicel CEA successfully provided extensive, permanent burn coverage in severely traumatized patients, proving an important adjunct to achievement of a high survival rate in a patient population whose prognosis previously had been poor. In our experience CEA appear to have a very high beneficial value in the management of bur ns >60% TBSA. In some cases studied it is very likely that CEA was a life-saving treatment.

Modern aspects of wound healing: An update

Wound healing is an area of cutaneous medicine in which there have been many recent advances. Interest has focused on the development of an in vitro reconstructed skin, although neither the commercially available products nor the products currently described in experimental studies are able to fully substitute for natural living skin. The substitution of the main component of each wound, the connective tissue matrix, is an advance. Once dermis is reconstructed, the covering of the wound surface with both in vitro expanded epidermis and autologous split-skin transplants is significantly easier and has an improved chance of success. Epidermal stem cells may facilitate functionality of the superficial part of such a system. New experimental and clinical trials are currently under way.

Cultured human keratinocytes on type I collagen membranes to reconstitute the epidermis

The development of new techniques and modifications to overcome some of the disadvantages in cultured keratinocyte grafting has been motivated by several well-known drawbacks in the use of cultured epithelial autografts such as long culture periods, lack of adherence, difficulty in handling, lack of dermal substrates, and high costs. Two recent insights have influenced further research. On the one hand, it has been shown that the use of undifferentiated proliferative cells in fibrin glue suspensions is effective in epithelial reconstitution. On the other hand, the enzymatic release of cells from the culture surfaces is a critical step leading to at least temporary destruction of anchoring structures of the cultured cells. In this study, we tried to combine these two aspects in an attempt to modify common modalities of keratinocyte transplantation. To avoid dispase dissolving of the cultured cells, keratinocytes were seeded onto bovine collagen type I membranes without feeder layers and under serum-free culture conditions. Subconfluent monolayers of cultured human keratinocytes were transplanted as an upside-down graft on collagen membranes (keratinocyte collagen membrane grafts [KCMG], n = 12) after 3 days of culture or as membrane grafts alone (n = 12) onto standard nude mice full-thickness wounds. Fully differentiated epidermis was found at 21 days after grafting KCMG with persistence of human keratinocytes. This study demonstrates that upside-down grafts of undifferentiated monolayers of keratinocytes on non-cross-linked bovine type I collagen membranes do lead to an early reconstitution of multilayered squamous epithelium with enhanced wound healing compared to the control group. The upside down KCMG grafting technique is able to transfer actively proliferative keratinocytes and simplifies the application compared to conventional epithelial sheet grafting.

The use of collagen-GAG membranes in reconstructive surgery

Porous collagen-glycosaminoglycan (PCG) membranes with a porous silicone elastomer coating have been useful as a scaffold for dermal replacement in burn victims. Critical physicochemical parameters of these membranes include pore size, cross-link density, the percentage of glycosaminoglycan, and the degree of banding of the collagen. These factors govern the immunobiological response. Optimizing these parameters can reduce inflammation, scarring, and contraction of wounds grafted with PCG membranes. PCG membranes are currently commercially manufactured (Integra, Integra Life Sciences, New Jersey) and available for clinical use. Because clinical outcomes have improved using these membranes for burn wound coverage, other skin reconstruction problems including scar resurfacing, keloids, treatment of donor sites, and treatment of chronic wounds can be considered as potential applications. This manuscript illustrates our early experience using Integra as a CG membrane for dermal replacement in reconstructive surgery. Our results indicate that CG membranes can lead to improved compliance and appearance compared to a meshed graft and may be sequentially placed in multiple layers to correct contour deformities. Also, in one case, we observed that, if placed on a wound bed with embedded skin epithelial cells, the PCG promotes epithelialization through the PCG matrix. The use of this material results in a supple integument with many similarities to normal skin.

Cellular artificial skin substitute produced by short period simultaneous culture of fibroblasts and keratinocytes

We developed a novel artificial skin substitute consisting of two collagen sponge layers with different pore sizes and cross-link densities. Fibroblasts suspended in 0.5 ml Dulbecco-modified Eagle's medium (DMEM) + 10% fetal bovine serum (FBS) were seeded on the lower dermal sponge layer, then epidermal collagen sponge and 0.1 ml suspension of keratinocytes in KGM were layered in this order. After a few hours, the medium was changed to DMEM + 5% FBS. These processes were carried out in one day, and the composite layers were then cultured by the air-liquid interface culture method. Three to five days after seeding, keratinocytes had grown to about ten layers, and fibroblasts had grown three-dimensionally into the lower dermal sponge layer. This novel cellular artificial skin substitute was grafted onto nude mice and took in 4 weeks. This skin substitute has the advantage of a shorter culturing period than previously cultured skins, and may be clinically useful for grafting that is urgently required in patients with severe generalised burns.

The control of epidermal stem cells (holoclones) in the treatment of massive full-thickness burns with autologous keratinocytes cultured on fibrin

BACKGROUND

Cell therapy is an emerging therapeutic strategy aimed at replacing or repairing severely damaged tissues with cultured cells. Epidermal regeneration obtained with autologous cultured keratinocytes (cultured autografts) can be life-saving for patients suffering from massive full-thickness burns. However, the widespread use of cultured autografts has been hampered by poor clinical results that have been consistently reported by different burn units, even when cells were applied on properly prepared wound beds. This might arise from the depletion of epidermal stem cells (holoclones) in culture. Depletion of holoclones can occur because of (i) incorrect culture conditions, (ii) environmental damage of the exposed basal layer of cultured grafts, or (iii) use of new substrates or culture technologies not pretested for holoclone preservation. The aim of this study was to show that, if new keratinocyte culture technologies and/or "delivery systems" are proposed, a careful evaluation of epidermal stem cell preservation is essential for the clinical performance of this life-saving technology.

METHODS

Fibrin was chosen as a potential substrate for keratinocyte cultivation. Stem cells were monitored by clonal analysis using the culture system originally described by Rheinwald and Green as a reference. Massive full-thickness burns were treated with the composite allodermis/cultured autograft technique.

RESULTS

We show that: (i) the relative percentage of holoclones, meroclones, and paraclones is maintained when keratinocytes are cultivated on fibrin, proving that fibrin does not induce clonal conversion and consequent loss of epidermal stem cells; (ii) the clonogenic ability, growth rate, and long-term proliferative potential are not affected by the new culture system; (iii) when fibrin-cultured autografts bearing stem cells are applied on massive full-thickness burns, the "take" of keratinocytes is high, reproducible, and permanent; and (iv) fibrin allows a significant reduction of the cost of cultured autografts and eliminates problems related to their handling and transportation.

CONCLUSION

Our data demonstrate that: (i) cultured autografts bearing stem cells can indeed rapidly and permanently cover a large body surface; and (ii) fibrin is a suitable substrate for keratinocyte cultivation and transplantation. These data lend strength to the concept that the success of cell therapy at a clinical level requires cultivation and transplantation of stem cells. We therefore suggest that the proposal of a culture system aimed at the replacement of any severely damaged self-renewing tissue should be preceded by a careful evaluation of its stem cell population.

Creation of an acellular dermal matrix from frozen skin

At present, one of the treatments of choice for closure of full-thickness skin loss is to use a cultured epidermal autograft when skin loss is extensive. In this study, we investigated a simple method of processing frozen surplus skin to produce an acellular, structurally intact, dermal matrix. First, the acellular dermal matrix prepared from normal human skin (ADM) we processed was observed using a transmission electron microscope and a scanning electron microscope. The matrix maintained the basement membrane complex and the extracellular matrix structure of the dermis despite frozen skin being used. Next, using an animal model, we transplanted the ADM and Pelnac, which is used as a contrast in full-thickness wounds onto nude rats. The dermal matrix supported fibroblast infiltration and neovascularization. These results suggest that skin processed by our simple method has the potential to be used as a dermal template together with the cultured epidermis in the closure of full-thickness wounds.

Pretreatment of human keratinocyte sheets with laminin 5 improves their grafting efficiency

Laminin 5 is essential in epithelial attachment to stromal tissues, suggesting that it might improve keratinocyte attachment in a variety of clinical situations. In this study, we examined the effect of exogenous laminin 5 upon the efficiency of transplantation of keratinocyte sheets in animal models. Keratinocyte sheets were prepared according to the method of Rheinwald & Green (1975). Purified laminin 5 was added to the sheets of group 1 (1.0 microg per cm2), Dulbecco's modified Eagle's medium alone was added to group 2. The sheets were grafted to the panniculus carnosus of nude mice (BALB/C nu/nu) (n = 12) and nude rats (Fisher 344) (n = 15). The take rate was assessed by measurement of the area of surviving epithelium at 7 d postgrafting. Laminin 5 bound the keratinocyte sheets of group 1. At 7 d postgrafting, the area of epithelialization of group 1 was significantly larger than that of group 2. Immunohistochemistry staining showed that collagen IV, laminin 5, and collagen VII stained more strongly at the dermal-epidermal junction in group 1 than in group 2. Integrin chains alpha6 and beta4 were similar in both groups. Electron microscopy at day 3 after grafting, showed the lamina densa of group 1 to be more continuous than in group 2. Pretreatment of cultured human keratinocyte sheets with laminin 5 improved the extent of epithelial coverage and increased the rate of neobasement membrane formation. The results suggest that laminin 5 promotes epithelial attachment by increasing the rate of basement membrane assembly.

Cultivation and transplantation of epidermal keratinocytes

Transplantation of autologous cultured keratinocytes is the most advanced area of tissue engineering which has clinical application in restoration of skin lesions. In vitro, disaggregated keratinocytes undergo activation and after adhesion and histogenic aggregation form three-dimensional epithelial sheets suitable for grafting on prepared wounds that provide a reparative environment. Epidermal stem cells survive and proliferate in culture, retaining their potential to differentiate and to produce neoepidermis. Reconstructed skin is physiologically compatible to split-thickness autografts. Autotransplantation of cultured keratinocytes is a promising technique for gene therapy. In many cases allografting of cultured keratinocytes promotes wound healing by stimulation of epithelialization. Banking of cryopreserved keratinocytes is a significant improvement in usage of cultured keratinocytes for wound healing. Skin substitutes reconstructed in vitro that have morphological, biochemical, and functional features of the native tissue are of interest as model systems that enable extrapolation to situations in vivo.

Novel living skin replacement biotherapy approach for wounded skin tissues

A novel living skin replacement (LSR) biotherapy concept, addressing the challenging problems related to tissue regeneration and wound healing, is presented for the treatment of skin burns, traumatic injuries and ulcerations. LSR combines elements of cell therapy along with those of tissue engineering to allow for the regeneration of wounded skin. It takes advantage of biodegradable microspheres onto which donor skin epidermal and dermal cells can be attached and expanded in vitro for subsequent direct application down to the deepest recesses of the wound bed. The key element of the biotherapy is the ability of the skin cells to migrate freely from the microspheres into the wound for regeneration of the tissues. The large surface to volume ratio of the microspheres allows for the delivery of appropriate cell numbers while minimizing the amount of biomaterial to be resorbed. This novel approach presents a number of advantages over existing therapies including facilitated cell manipulations, ease of storage and transportation, rapid clinical intervention due to the elimination of any surgical suturing or stapling, and a more natural three-dimensional tissue remodeling and anatomical compliance. Preliminary in vitro and in vivo evidence of the LSR functionality and its potential benefits is presented.

The requirement for basement membrane antigens in the production of human epidermal/dermal composites in vitro

The importance of a dermal element when providing permanent wound cover for skin loss has become evident as the shortcomings of pure epidermal grafts are recognized. We are developing a skin composite formed from sterilized human de-epidermized acellular dermis, keratinocytes and fibroblasts with the ultimate aim of using this composite to cover full-thickness excised burn wounds. These composites can be prepared with or without basement membrane (BM) antigens initially present on the dermis. This study investigates the importance of retaining BM antigens on the dermis to the production and appearance of these composites in vitro. Skin composites prepared from dermis with BM antigens either present or absent initially were studied throughout 3 weeks. Composites with BM antigens present initially were significantly better than those initially lacking BM antigens in: (i) the degree of epithelial cell attachment to the underlying dermis (hemidesmosomes were seen only in the former); (ii) the morphology of the epithelial layer; (iii) the consistent presence of collagen IV and laminin and the increasing expression of tenascin; and (iv) the amount of soluble collagen IV and fibronectin detected in the conditioned media. We conclude that an initial BM antigen template is vital in this skin composite model for the attachment and differentiation of the epithelial layer and for the subsequent remodelling of the BM in vitro.

Skin substitutes from cultured cells and collagen-GAG polymers

Engineering skin substitutes provides a potential source of advanced therapies for the treatment of acute and chronic wounds. Cultured skin substitutes (CSS) consisting of human keratinocytes and fibroblasts attached to collagen-glycosaminoglycan substrates have been designed and tested in preclinical and clinical studies. Cell culture techniques follow general principles of primary culture and cryopreservation in liquid nitrogen for long-term storage. Biopolymer substrates are fabricated from xenogeneic (bovine) collagen and glycosaminoglycan that are lyophilised for storage until use. At maturity in air-exposed culture, CSS develop an epidermal barrier that is not statistically different from native human skin, as measured by surface electrical capacitance. Preclinical studies in athymic mice show rapid healing, expression of cytokines and regulation of pigmentation. Clinical studies in burn patients demonstrate a qualitative outcome with autologous skin that is not different from 1:4 meshed, split-thickness autograft skin, and with a quantitative advantage over autograft skin in the ratio of healed skin to biopsy areas. Chronic wounds resulting from diabetes or venous stasis have been closed successfully with allogeneic CSS prepared from cryopreserved skin cells. These results define the therapeutic benefits of cultured skin substitutes prepared with skin cells from the patient or from cadaver donors. Future directions include genetic modification of transplanted cells to improve wound healing transiently or to deliver gene products systemically.

Cultivation of human keratinocyte stem cells: current and future clinical applications

Cultured human keratinocytes have a wide spectrum of clinical applications. Clinical results reported by several investigators are, however, contradictory. In this review, the authors discuss the biological and surgical issues which play a key role in the clinical outcome of cultured epidermal autografts used for the treatment of massive full-thickness burns. The importance of cultivation of epidermal stem cells and of their transplantation onto a wound bed prepared with donor dermis is emphasised. The paper also reviews recent data showing that: (i) cultured epidermal autografts bearing melanocytes can be used for the treatment of stable vitiligo; (ii) keratinocytes isolated from other lining epithelia, such as oral, urethral and corneal epithelia, can be cultivated and grafted onto patients suffering from disabling epithelial defects; (iii) keratinocyte stem cells can be stably transduced with retroviral vectors and are therefore attractive targets for the gene therapy of genodermatoses.

In vitro reconstruction of a human capillary-like network in a tissue-engineered skin equivalent

For patients with extensive burns, wound coverage with an autologous in vitro reconstructed skin made of both dermis and epidermis should be the best alternative to split-thickness graft. Unfortunately, various obstacles have delayed the widespread use of composite skin substitutes. Insufficient vascularization has been proposed as the most likely reason for their unreliable survival. Our purpose was to develop a vascular-like network inside tissue-engineered skin in order to improve graft vascularization. To reach this aim, we fabricated a collagen biopolymer in which three human cell types keratinocytes, dermal fibroblasts, and umbilical vein endothelial cells were cocultured. We demonstrated that the endothelialized skin equivalent (ESE) promoted spontaneous formation of capillary-like structures in a highly differentiated extracellular matrix. Immunohistochemical analysis and transmission electron microscopy of the ESE showed characteristics associated with the microvasculature in vivo (von Willebrand factor, Weibel-Palade bodies, basement membrane material, and intercellular junctions). We have developed the first endothelialized human tissue-engineered skin in which a network of capillary-like tubes is formed. The transplantation of this ESE on human should accelerate graft revascularization by inosculation of its preexisting capillary-like network with the patient's own blood vessels, as it is observed with autografts. In addition, the ESE turns out to be a promising in vitro angiogenesis model.

Tissue engineering of skin

The skin plays a crucial role in protecting the integrity of the body's internal milieu. The loss of this largest organ is incompatible with sustained life. In reconstructive surgery or burn management, substitution of the skin is often necessary. In addition to traditional approaches such as split- or full-thickness skin grafts, tissue flaps and free-tissue transfers, skin bioengineering in vitro or in vivo has been developing over the past decades. It applies the principles and methods of both engineering and life sciences toward the development of substitutes to restore and maintain skin structure and function. Currently, these methods are valuable alternatives or complements to other techniques in reconstructive surgery. This review article deals with the evolution and current approaches to the development of in vitro and in vivo epidermis and dermis.

Characterization of epidermal wound healing in a human skin organ culture model: acceleration by transplanted keratinocytes

Few data are available on early regeneration of human epidermis in vivo. We have established a supravital skin organ culture model for epidermal wound healing by setting a central defect (3 mm diameter) in freshly excised skin specimens and culturing under air exposure. Re-epithelialization was followed for up to 7 d by histology and immunohistologic analysis of various markers for differentiation and proliferation. In 12 of 19 cases (63%; 5% fetal calf serum) or six of 21 cases (29%; 2% fetal calf serum), the wounds were re-epithelialized spontaneously after 7 d. After transplantation to the wounds of 1-2 x 10(6) dissociated allogenic cultured epidermal or about 1 x 10(6) autologous outer root sheath keratinocytes, 18 of 21 cases (86%; 5% fetal calf serum) or 17 of 21 cases (81%; 2% fetal calf serum) were healed within the same period. Histologically, early neoepithelium (3 d) was disordered after keratinocyte transplantation, whereas later (7 d) it had gained a more ordered stratification, exhibiting a thin discontinuous granular and a compact horny layer. At this stage, not only hyperproliferative (CK 6) but also, abundantly, maturation-associated cytokeratins (CK 1, CK 10) were detected immunohistochemically. Analyses of regenerated epidermis after transplantation of (i) keratinocytes labeled in vitro with BrdU and (ii) heterosexual keratinocytes by immunohistochemistry and fluorescence in situ hybridization for the Y chromosome, respectively, clearly showed that external keratinocytes are physically integrated into the regenerated epidermis and extendedly contribute to its formation. The data presented here demonstrate improvement and acceleration of epidermal re-epithelialization by transplantation of keratinocytes.

Vascularized collagen-glycosaminoglycan matrix provides a dermal substrate and improves take of cultured epithelial autografts

Cultured epithelial autografts are an important adjunct in treating severely burned patients, greatly expanding the epidermis using a small donor site. Problems with cultured epithelial autografts include the time delay to culture cells to confluence and variable take on full-thickness wounds. Dermal allografts have been used as a substrate to improve the take of cultured epithelial autografts. This study examined the effect of a vascularized collagen-glycosaminoglycan matrix as a substrate for cultured epithelial autografts. The matrix was grafted onto 12 full-thickness wounds in Yorkshire pigs and allowed to vascularize for 10 days. The cultured epithelial autografts were applied over the vascularized collagen-glycosaminoglycan matrix (n = 12) or onto freshly excised full-thickness wounds (n = 10). Gross and histologic observations were made over a 3-week period. Gross observations at 7 days indicated cultured epithelial autografts to have nearly complete confluence when applied to wounds treated by collagen-glycosaminoglycan, whereas cultured epithelial autografts applied to freshly excised wounds did not take. Gross determination of epithelial confluence was verified by histologic analysis of randomly selected wounds. Histologic epithelial confluence of cultured epithelial autografts on collagen-glycosaminoglycan (98 +/- 4 percent) was significantly greater than that on full-thickness wounds (4 +/- 10 percent). Electron microscopy of the cultured epithelial autografts/collagen-glycosaminoglycan construct demonstrated anchoring fibrils at the dermal-epidermal junction at day 7. The neoepidermis of wounds treated by cultured epithelial autografts/collagen-glycosaminoglycan was hyperplastic at day 7 but developed a normal maturation sequence by 21 days. Results from this study suggest that vascularized collagen-glycosaminoglycan matrices produce a favorable substrate for cultured epithelial autografts and may improve cultured epithelial autografts take in burn patients.

Advantage of the presence of living dermal fibroblasts within in vitro reconstructed skin for grafting in humans

Methods for serial cultivation of human keratinocytes can provide large quantities of epidermal cells, which have the potential of restoring the vital barrier function of the epidermis in extensive skin defects such as burns. To investigate the value of combining an epidermis with a dermal component, fibroblasts originated from the superficial dermis were used to seed a collagen lattice as described by E. Bell (dermal equivalent). Beginning in 1981, we grafted 18 patients (burns and giant nevi) using 35 grafts 10 x 10 cm in size. In the course of this work, the original technique was modified and improved as experience was gained. We began by using small skin biopsy samples as a source of keratinocytes cultured on a dermal equivalent before grafting in a one-step procedure, but this gave poor cosmetic results, because of a nonhomogeneous epidermalization. We then chose to cover the graft bed using a two-step procedure. The first step consisted of grafting a dermal equivalent to provide a dermal fibroblast-seeded substrate for subsequent in vivo epidermalization by cultured epidermal sheets. Whatever the epidermalization technique used, a living dermal equivalent applied to the graft bed was found to reduce pain, to provide good hemostasis, and to improve the mechanical and cosmetic properties of the graft. A normal undulating dermal-epidermal junction reappeared by 3 to 4 months after grafting and elastic fibers were detectable 6 to 9 months after grafting. As a result of the biosynthesis of these products, the suppleness (e.g., elasticity) of the grafts was closer to that of normal skin than the cicatricial skin usually obtained with epidermal sheets grafted without the presence of living dermal cells. This rapid improvement of the mechanical properties of the graft could be attributed to the presence of fibroblasts cultured from the dermis and seeded into the collagen matrix.

Organized skin structure is regenerated in vivo from collagen-GAG matrices seeded with autologous keratinocytes

A well-characterized collagen-glycosaminoglycan matrix (CGM) that has been shown to function as a dermal analog was seeded with freshly disaggregated autologous keratinocytes and applied to full-thickness wounds in a porcine model. CGM were impregnated with 50,000 keratinocytes per cm2, a seeding density that produces a confluent epidermis within 19 d post-grafting and affords a 60-fold surface expansion of the donor epidermis. In this study, the temporal sequence of events in epidermal and neodermal formation was analyzed histopathologically and immunohistochemically from 4 to 35 d post-grafting. The epidermis was observed to form from clonal growth of individual keratinocytes into epithelial cords and islands that gradually enlarged, coalesced, differentiated to form large horn cysts, and finally reorganized at the graft surface to form a fully differentiated, normally oriented epidermis with rete ridges. Simultaneously, a neodermis formed from migration of endothelial cells, fibroblasts, and macrophages into the CGM from the underlying wound bed, resulting in formation of blood vessels, the production of abundant extracellular matrix, and the degradation of the CGM fibers, respectively. Gradually, the stromal cellularity of the CGM decreased and collagen deposition and remodeling increased to form a neodermal connective tissue matrix beneath the newly formed epidermis. Complete dissolution of the CGM occurred, partly as a result of degradation by an ongoing foreign-body giant cell reaction that peaked at 8-12 d post-grafting, but neither acute inflammation nor evidence of immune stimulation were observed. Within 1 mo, many structural components of normal skin were reconstituted.

In vitro engineering of human skin-like tissue

Coverage of large, full-thickness burns presents a challenge for the surgeon due to the lack of availability of the patient's own skin. Currently, tissue engineering offers the possibility of performing a suitable therapeutic wound coverage after early burn excision by using cultured keratinocyte sheets supported by a dermal layer. The aim of this study was to develop and characterize a skin substitute composed of both epidermal and dermal elements. For this purpose we grew keratinocytes and fibroblasts separately for 15 days within two different types of biomaterials. Cells then were co-cultured for an additional period of 15 days, after which samples were taken and processed with either classic or immunohistochemical stainings. Results showed that (1) human fibroblasts and keratinocytes can be cultured on hyaluronic acid-derived biomaterials and that (2) the pattern of expression of particular dermal-epidermal molecules is similar to that found in normal skin. The data from this study suggest that our skin equivalent might be useful in the treatment of both burns and chronic wounds.

Effect of keratinocyte seeding of collagen-glycosaminoglycan membranes on the regeneration of skin in a porcine model

A collagen-glycosaminoglycan matrix, impregnated with autologous keratinocytes, was applied as island grafts onto full-thickness porcine wounds to determine whether complete epidermal coverage could be achieved in a single grafting procedure. Twenty-four grafts with seeding densities ranging from 0 to 3,000,000 cells/cm2 were used to determine the kinetics of epidermal coverage. The time sequence of epidermal formation was then studied between days 14 and 28 using four additional grafts, each seeded with a density of 500,000 cells/cm2. Autologous keratinocytes proliferated as the collagen-glycosaminoglycan matrix was vascularized to form a confluent epidermis by 2 weeks in matrices seeded with at least 100,000 cells/cm2. The epidermal thickness and the number of keratinocyte cysts observed in the neodermis at 2 weeks increased linearly with the logarithm of the seeding density. Sequential analysis of neoepidermis showed the nascent epidermis to be hyperplastic, parakeratotic, and focally lacking in granular layer differentiation at 2 weeks. After 2 weeks, it underwent normal maturation and differentiation. Irrespective of seeding density at 2 weeks the collagen-glycosaminoglycan matrix was well vascularized, contained a dense cellular infiltrate, and was almost completely degraded. These studies demonstrate that seeded keratinocytes proliferate and differentiate to form a confluent epidermis by 2 weeks in matrices seeded with at least 100,000 cells/cm2.

Nursing management of skin grafts and donor sites

Skin grafting is one of the most commonly used techniques in plastic and reconstructive surgery. The patient undergoing split-thickness skin grafting may pose a variety of wound care problems for the nurse. The issues that may need to be addressed include: the reasons for grafting; type of graft used; preoperative and postoperative care of the recipient and donor sites; and the provision of general measures required to promote wound healing and successful graft take for the patient.

Skin banking in the UK: the need for proper organization

Skin banking was set up in Sheffield in 1991 to provide a readily available source of allograft material to be used both for research purposes and also as a means of providing immediate wound cover for major burns patients. Once skin was available, however, clinical demand for it both within and outside Sheffield, outstripped the resources to run the bank. Logistical difficulties were encountered in the day to day running of the bank. These revolved around shortage of staff available for harvesting, the relative lack of public awareness of skin donation, shortage of banked skin as the bank became more widely known and lack of space and finance to expand. The decision was made to transfer the now established skin bank to the National Blood Service where it now operates with staff and resources dedicated specifically to this purpose. Experience leads to the suggestion that there is a clinical need for allograft skin in the UK which is not being met at the present time. There is a need for dedicated properly resourced skin banks and for the Department of Health to introduce regulation, monitoring and inspection of skin bank facilities in order to safeguard standards.

Therapeutic gene delivery to the skin

The skin represents a site for treatment of cutaneous and systemic disease and is the most accessible somatic tissue for therapeutic gene transfer in humans. Monogenic hereditary skin diseases, such as ichthyosis and epidermolysis bullosa subtypes, and disorders characterized by low levels of polypeptides in the systemic circulation, are current central foci of efforts in cutaneous-gene transfer. Additional efforts center on the treatment of wounds and malignancies. Recent developments in models of gene delivery to the skin underscore key challenges that must be met before successful treatment of human disease by cutaneous gene delivery can be achieved.

Optimized mesh expansion of composite skin grafts in rats treated with direct current

BACKGROUND

The purpose of this study was to determine the optimum autoepidermal and allodermal expansion ratio of each component of a meshed composite skin graft (MCSG) that would lead to successful healing.

METHODS

Male Sprague-Dawley rats were used as hosts of the MCSG and donors of autologous tissue. Male ACI rats were used as donors of allodermis. MCSGs with open meshed area (autoepidermal/allodermal) of 9:1/1.5:1, 9:1/3:1, 9:1/6:1, or 6:1/6:1 were applied to full-thickness skin defects and treated with a silver nylon dressing (SN) or SN with direct current (DC). Wound size, hair regrowth, and thickness of dermal layer were evaluated at 3 months.

RESULTS

MCSGs of 9:1/1.5:1, 9:1/3:1, and 6:1/6:1 mesh ratios healed completely within 3 months with no difference in wound size between SN dressing groups or DC-treated groups. Application of DC reduced MCSG contraction and stimulated regrowth of hair.

CONCLUSION

Fresh autoepidermis can be expanded 6:1 on a 6:1 allodermis or 9:1 on a 3:1 allodermis and achieve successful wound healing.

Analysis of cellular and decellular allogeneic dermal grafts for the treatment of full-thickness wounds in a porcine model

BACKGROUND AND METHODS

The need for a reliable skin substitute to improve burn treatment has been long apparent. We have investigated the use of cryopreserved cellular and decellularized porcine allogeneic dermal grafts (CADGs or DADGs) in conjunction with an overlying thin split-thickness autograft (STSG) in a one-step technique. Control mirror-image wounds were treated with thin STSG alone. Autograft "take" rates and wound contraction were determined; biopsies were taken at weeks 2, 5, and 8, and blinded scar assessment was performed at week 10.

RESULTS

The percent take of autografts overlying CADGs or DADGs was comparable to that of control sites (83.0 +/- 8.3% vs. 81.1 +/- 11.5% for CADG vs. control; 93.2 +/- 7.6% vs. 90.2 +/- 11.1% for DADG vs. control). CADGs did not alter wound contraction or cosmetic outcome. By contrast, DADG treatment inhibited wound contraction (42.9 +/- 17.8% vs. 30.9 +/- 10.4% contraction for control vs. DADG at week 10; p < 0.017) and significantly improved cosmetic outcome in 10 of 12 paired wounds (p < 0.012).

CONCLUSION

CADGs and DADGs permitted simultaneous engraftment of an overlying thin STSG. Although CADGs had no effect on wound contraction and cosmetic outcome, DADGs significantly reduced wound contraction and improved cosmetic outcome of full-thickness wounds in a porcine model. The use of DADGs may represent a potential improvement in burn care.